Prior art antennas have been produced having electrical characteristics which are known to be 150 ohms resistive when the total length of wire is one-half wavelength in the vertical position. These antennas are themselves basically grounded, vertically polarized and exhibit an omnidirectional radiation pattern and are called folded monopole antennae.
Additional prior art antennas include those described with respect to U.S. Pat. Nos. 1,438,290 to Beakes; 2,169,377 issued to Walter; 2,508,648 issued to O'Brien; 2,573,682 issued to Barret; 2,702,345 issued to Walter; 3,376,577 issued to Kennedy; 3,400,402 issued to Gallagher and 3,530,474 issued to Campbell. For example, the patent to Campbell describes an antenna which utilizes loading in the form of capacitance, induction, or both, for shortening the physical antenna length or height relative to the electrical length. Two insulators are provided and, if they move upward, the length of various wires will increase, thus increasing the capacity to ground of the top loading conductors.
Walter '345 discusses an antenna having a vertically disposed portion and a horizontally disposed portion, wherein the length of the vertically disposed portion can be changed. As illustrated in Figure 14, a tower supports a pulley and a block carries a second pulley which receives a cable secured to an insulator. This cable can act as an antenna and has a vertically disposed portion and a horizontally disposed portion between various pulleys. Changes in the length of the vertically disposed portion of the cable can be effected by lengthening or shortening a rope attached to a different pulley. Impedance matching will be effected by changing the length of the vertically disposed portion of the cable.
The additional patents mentioned hereinabove describe various antennas having a variable length, utilize a pulley system or are of general interest.
However, none of these patents describe an antenna whose resistance is reduced to 50 ohms nominal by creating a triangularly shaped antenna having a top flat portion, and further the total effective length is one half wavelength. Furthermore, no reference is known wherein the proportion of wire length to the height of the base portion of the triangular antenna is controlled automatically by changing the total length of the antenna wire as well as the distance between the flat portion of the antenna wire and the ground.